Oscillatory fluid stream driven sonic generator with elastic autoresonator



Nov. 26, 1963 A. G. OSCILLATORY FLUID STREAM BODINE DRIVEN SONIC GENERATOR WITH ELASTIC AUTORESONATOR Filed Malrch 3l, 1960 L @i y S y v/ m (l, W W/ ffz 5 E Blefadzme W//zV///` f'f'w @Y @5- United States Patent O 3,llll,931 OSCILLATRY FLUED STREAM DRVEN SGNIC GENERATOR WTH ELASTC AUTRESONATR Albert G. Bodine, Sherman Gaite, Calif. (7 899 Woodley Ave., Van Nuys, Calif.) Filed Mar. 31, i960, Ser. No. @,073 11 Claims. (Qi. 116-137) This invention relates generally to resonant acoustic generators useful as sound sources in many applications of sonic processing, such as accelerating chemical reactions, sonic cleaning, actuation of sonic drills, etc. The invention is more particularly concerned with a novel sonic generator involving a type of fluid stream oscillator having a fluid stream either liquid or gas, periodically deflected between two flow paths under control of an elastic resonator.

An object of the invention is the provision of a novel and useful sonic generator, and a further object is the provision of a novel and useful sonic generator of the class mentioned which is controlled and stabilized as to periodicity by incorporation of an elastic resonator.

A still further object is the provision of a sonic generator of the class mentioned which is without valves, and which is capable of embodiment for low or high frequency operation, from Very low power to very high power, is highly reliable, particularly by reason of elimination of valves, and which has good dynamic lluid to mechanical energy conversion efficiency by reason of utilization of elastic resonance for frequency control.

The generator of the invention, speaking generally, establishes a lluid stream provided with two alternate flow paths between which it may be deflected by periodically iluctuated lateral control pressure, with the periodicity of control pressure lluctuation controlled by an elastic resonator energized from the periodically deflected iluid stream. rThe resonator is contrived to function as a sonic source.

The invention will be better understood from the following detailed description of a number of illustrative embodiments, reference for this purpose being had to the accompanying drawings, in which:

FIG. l is a diagrammatic side elevational View of one embodiment of the invention, portions being shown in longitudinal medial section;

FIG. 2 is a diagrammatic side elevational view of another embodiment of the invention, portions being shown in longitudinal medial section;

FlG. 3 is a longitudinal medial sectional View through another embodiment of the invention, the forward portion of the resonator rod being broken away;

FiG. 4 is a transverse section on line 4 4 of FlG. 3; and

FlG. 5 shows the forward portion of the resonator rod broken away in FlG. 3.

With reference first to FIG. l, numeral lll designates a centrifugal pump or blower discharging into a conduit il whose walls are constricted at l2 to form a nozzle 13. Beyond nozzle 13, the walls of the conduit form a split, providing two branch conduits 14 and 15. Branch lll expands along its lengthin the form substantially of an exponential horn lle, while branch l5 leads back to the intake of pump il). The large end of horn le is closed by a domed, preferably thin-walled, metallic elastic diaphragm 17, bolted to a flange i8 on the periphery of the horn. Fluid may be introduced to the system as by means of pipe i9 leading into branch conduit l5 and provided with shut-off valve 2b.

Horn 16, with its closure i7, and relatively narrow neck region 21, filled with an elastic lluid medium, functions in the nature of a Helmholtz resonator. Thus, when a fluid stream is blown into or past its neck region, iluid oscillation takes place in its neck region at a critical Mlee resonant frequency determined by its dimensions. This oscillation is a very definite type, requiring and utilizing elastic compression and rarefaction of the fluid, or in other words, the selected frequency of acoustic resonance. rl`he amplitude of lluid particle oscillation velocity is at a maximum in the neclr region. This region of maximized Velocity oscillation may be referred to as a velocity antinode region. ln the large end of the chamber 22 of the resonator, as at 23, adjacent diaphragm i7, velocity oscillations are at a minimum, but substantial pressure oscillations are experienced. This region 23 is known as a velocity node, or pressure antinode. Diaphragm i7 is capable of being set into elastic vibration under the influence of the pressure oscillations within region 23, and its exterior surface functions as a sound radiator. If the iluid beyond diaphragm i7 is of about the same acoustic impedance as the lluid within cavity 16, diaphragm 17 will become almost an acoustic window, except for the resonance in i6.

A iluid conduit 25 communicates the neck region 21 (velocity antinode) of the chamber with the interior of conduit 1l at a point within or just beyond the throat of nozzle 13, the conduit 25 opening laterally into conduit il via an orifice 25a located on the side of conduit ll that leads to the outer side of branch ld, as shown. Conduit 25 preferably has a scoop-type entrance orifice 26 within the neck region of the resonator, facing upstream therein with reference to the fluid ilow direction through nozzle i3.

Somewhat similarly, a iluid conduit 27 communicates a point in branch conduit 15, located somewhat downstream from the point of branching of conduit 11, with the interior of conduit il, at or just beyond the throat of nozzle i3, opening laterally into conduit ll via an oriilce 27a located in the side of said conduit opposite from orifice 25a. Conduit Z7 also has a scoop-type entrance orifice 28 facing upstream in conduit branch 15. In this embodiment the scoop orifices 26 and Ztl are preferably made as small as possible, commensurate with the conduits 25 and 27, and with the requirement for acoustic feedback` control subsequently to be explained.

As a preferred but optional feature, two auxiliary control conduits 25 and 29 open laterally into conduit l on opposite sides thereof, adjacent orifices 25a and 27a, respectively, and longitudinally alined therewith. Conduits 28 and 29 can be supplied with lluid pressure energy from any suitable source, using conventional pumps, etc., not shown.

The iluid stream issuing from nozzle 13 can be dellected to flow through branch i4 and into the resonator chamber 22, or into branch conduit l5, depending upon relative lateral fluid pressures exerted thereon via conduits 25 and 27, or 28 and `29, or in response to the resultant ol' lateral pressures or pressure pulses established in these four conduits. Basically, the fluid stream will idellect away from a source of lateral iluid pressure. For example, if the pressure in conduit 29 exceeds the pressure in conduit 28, and assuming for the moment that conduits 25 and 27 are not supplying pressure to the stream, the stream will be deilected to llow into branch i4, `and the chamber of the resonator, whereas if the pressure in conduit 28 exceeds that in conduit 29, with the same assumption as regards conduits 25 and Z7, the fluid stream will lbe deflected to flow into branch conduit l5. Similarly, a pressure pulse from conduit 25 in excess of any pressure pulse from conduit 27, with the pressures in conduits 28 and Z9 equal, or with 2S and 29 eliminated, deilects Ithe fluid stream into branch conduit i5, whereas a pressure pulse from conduit 27 in excess of any pressure pulse from `conduit 25 results in the fluid stream being dellected into branch ld leading to the resonator chamber.

Assume now that a lluid stream is being pumped around the system by means of pump iti, fluid flow either into or past the branch 14;- leading into the resonator chamber will set the fluid body in said chamber into oscillation at the natural resonant frequency of the resonator. As described earlier herein, fluid oscillation then commences in neck region 21, as indicated by the doubleheaded arrow a. Assuming7 fluid flow from nozzle 13 into the resonator, on each forward pulse, for example, fluid pulses into orifice 25, through conduit `and is delivered through orifice 25a as a pressure pulse impinging laterally against the fluid stream passing through the nozzle i3. Assuming that fluid has been flowing into branch 14- and the resonator, such lateral pressure pulse deflects the fluid stream away from branch 14 and into branch l5. A further feature of the invention is that the conduit 25 is acoustically tuned, as by adjustment of its length and/or cross sectional area, in relation to the density of the fluid, to have such acoustic impedance as will introduce a time delay between the instant at which the pressure pulse enters the orifice 26 and the instant at which the pressure pulse is delivered from hole 25m and acts laterally against the fluid stream to shift it to branch l5. Accordingly time is afforded for a fully developed pressure rise within the resonator chamber prior to deflection of the stream into branch 15. In other words, the half cycle during which fluid flows into the resonator chamber is afforded time for completion. The described pressure rise within the resonator chamber distends elastic diaphragm i7, causing a wave of compression to be radiated into whatever sound transmission medium, liquid or gaseous, may be in contact therewith. The fluid stream being diverted away from branch 14, the pressure in the resonator falls, and fluid flow in the resonator is then in the reverse direction, i.e., outward of the neck region of the resonator. Diaphragm 17 then moves rearwardly, and a pulse of rarefaction is radiated therefrom. lt may here be noted that this outflow cycle from the acoustic resonator is aided by the aspirating action of `flow into branch i5.

In the meantime, with fluid flow now through branch 15, a pressure pulse is delivered via orifice 28, conduit 27 and orifice 27a laterally against the `fluid stream through nozzle 13, causing the stream to be deflected over so as to flow again into branch lli and the resonator chamber. Conduit 27 is also acoustically tuned, by adjustment of its length and/ or cross section, in relation to the density of the fluid in the system, so as to have a time delay such that the last described switch-over of the fluid stream occurs near the termination of the reverse flow half cycle of the resonator chamber. Fluid then again flows into the resonator chamber, and the described cycle is repeated.

The described tuning of the conduits 2S and 27 is well within the skill of those skilled in the acoustic art, it being only necessary to point out that the time delays introduced are to be such as to effect back and forth switch-over of the fluid stream at half-cycle intervals of the resonant frequency of the resonator. It is important to note that, with a system employing an acoustic resonator such as 14, the acoustic pulses transmitted through conduits 2S and 2.7 need be only elastic pulses, and thus there need be no net flow through 25 and 27.

A further advantage may be realized by tuning the elastic diaphragm to have a resonant frequency matched to the resonant frequency of the resonator. The acoustic Q of the system is thereby increased, and the cycle further stabilized.

The two auxiliary contact conduits 2,3 and 29 are useful in initiating the cycle. Timed pulses may be delivered therethrough to periodically deflect the fluid stream at the start, until the resonant cycle is built up and stabilized.

A well designed system, however, will be self starting. The conduits 28 and 2.9 may also be used to effect other control functions, such, for example, as temporarily constraining the flow to branch l5 in order to interrupt sound radiation from the resonator, or to effect pulsed radiation.

It has been found that the switch-over operation of the device of FIG. l can be explained by taking into account well known hydrodynamic phenomena concerned in fluid flow over a hydrodynamic surface such as an airplane wing. Thus the flow, once started along the lower side of the conduit passage at l2, tends to cling thereto in the manner of the flow along a hydrofoil. In conformity with the law of Bernoulli, a low pressure is created in the region of the opening 27a by this flow, and the flow stream tends to continue along this surface. Then if an elevated pressure, such as a pulse as described above, is delivered to region 27a, the flow will then quickly flop over to carry along the opposite shaped side of the conduit wall, past the opening 25a..

Reference is next directed to FIG. 2, showing a dual resonator form of apparatus in accordance with the invention. ln this instance, pump 33 delivers fluid under pressure to discharge conduit 31 having a constriction at 32 forming a nozzle 33. Beyond the nozzle, the conduit 31 has two branches 34 and 35, each expanding to form a horn of substantially exponential form, as indicated by reference numerals 36 and 37, respectively. The large ends of the horns 36 and 37 are closed by elastic resonator plates 3S and 39, respectively, capable of elastic transverse vibration, and tuned to the resonant frequency of the resonator chambers 4() and dil. The resonator plates 38 and 39 are spaced apart from one another by a half-wave length distance of the sound wave radiated therefrom, measured in the fluid transmission medium in contact therewith. Since, as will appear, the two resonator plates operate with phase difference, this provision is required in order to prevent wave cancellation by dipole action. The fluid is returned to the pump by way of discharge conduit 42 leading from the large ends of the two resonators, and by discharge conduit 43, leading from the neck regions thereof, all of which join a `return pipe 4S leading back to the intake of pump 33.

Pulse conduits 45 and 47 intercommunicate the neck regions of resonators 4d and 4l with diametrically opposite points of conduit 31 near to nozzle 33, as indicated, the points of communication of said conduits with the conduit 3f being on the two sides of the latter in correspondence with the directions of divergence of the two branch passages. The acoustic impedance of acoustic wave-guide conduits i6 and 47 are `adjusted to afford a tuning thereof, at the resonant frequencies of the resonators, such as will introduce a time delay as explained in connection with FIG. 1. Final best adjustment can be obtained by building `a prototype and adjusting the lengths of these conduits, such as by scoop location, to obtain most vigorous resonance. Subsequent copies of the machine can then be made simply to these dimensions. Operation is essentially as in FIG. l, with the exception that both branches of the conduit lead into resonator chambers, with net flow return from the resonator chambers rather than from `a separate conduit such as 15 in FIG. l.

It will be seen that the fluid stream is deflected alternately into one resonator chamber and then the other, timed by `acoustic pressure pulses returned from the neck regions of the resonators to the throat region of the conduit. Appearance of a lateral pressure pulse on one side or the other of the fluid stream functions in switching the latter between the two resonators; and the pressure pulse in each case is delivered to fully switch the fluid stream in proper phase so as to accomplish maximum periodic resonant pressure rise of the elastically compressible fluid within the corresponding resonator.

This invention employs the acoustic elastic properties of media, either fluid or solid such as in the examples illustrated, `and therefore actual net fluid flow, if any, is incidental to the invention. In fact, the fluid stream from a pump is merely a means for delivering fluid energy to the acoustic system. The actual operation of the invention relies upon acoustic elastic vibration, such as compression and expansion, and the essential fluid flow may only osciilate (or pulse) in place; such as in the region 21 of FIG. 1. In FIG. 2 the net uid stream does not determine the elastic cycle.

The fluid return pipes 42 and r#i3 for each resonator may be used together or either may -be omitted.

The relatively heavy tuned resonator plates 313 and 39 further improved the acoustic Q of the system and thereby increase the stability of the cycle.

FIGS. 3 to 5, inclusive, show Aanother embodiment of the invention, using, as a resonator element, a half-wavelength, elastic, longitudinally vibratory rod or bar. A tubular member S with a fluid flow passage 51 Itherethrough has at one end internal threads y52 for coupling of an intake conduit leading from 'a fiuid pump. Beyond threads 52, the passage 5,1 is constricted to form a nozzle 53, and, as shown, the passage 51 continues on past nozzle 53 with uniform :diameter at 54, :and with a final flare 55 to the end of member 50. At this end of the member there is joined thereto, as by screw threads S6, a relatively long, forwardly reaching sleeve 57. The forwardly extremity of `this sleeve 57 has an internal shoulder 58 supporting, by shrink lit, the mid point of a relatively long tubular elastic bar 60.

A fluid conduit 62 has a portion 63 extending through the bore of tubular bar 6l) with small annular clearance therewithin, and has a flattened or semicylindric portion 64 received within passage portion 54 and deflected so as to lie adjacent one surface thereof, being secured to the wal-l surface of bore 54 by welding or brazing, as indicated at 65. Conduit 64 has a narrow mouth 66 facing upstream, and located just beyond nozzle 53. The opposite end ofthe conduit 62 is opened, and discharges forwardly, through the forward open end of tubular rod 601.

Laterally oriented pressure pulse orifices are provided to cause the duid stream from nozzle 'S3 to pass either through the flow path 68 outside of and to one side of the portion 64 of lconduit 62, or into the conduit portion 64. For this purpose, longitudinal bores 69 and 79 are drilled through member -to one side of fluid passage 51 for the principal length of the latter but opening through the flared portion thereof. The forward ends of `these bores are closed by means of plugs 71. The bores 69 and 79 intersect transverse -bores 72 and 73 drilled inwardly into communication with passage S1 somewhat beyond the nozzle constriction at 531. The outer ends of these bores 72 and 73 are also closed by means of plugs 74. Scoop type port tubes 77 and 7S are set into the flared walls 65, so as to communicate with bores y69 and 7d, rrespectively, and the scooped ends of these port tubes are positioned in the fluid flow streams outside and inside the conduit 612 respectively, both facing upstream.

The distance from the discharge side of nozzle 53 to the adjacent end 8) of tubular resonator bar 60 is preferably made effectively equal to a quarter-wavelength, or `odd multiple thereof, of a sound wave in the fluid medium circulated through the system, which in the instance of V this embodiment of the invention is normally a liquid. lt might be noted that while a one-quarter wavelength distance is preferable, any odd multiple of a quarterwavelength may be used. The length of tubular bar 80 is preferably m-ade equal to a half-wavelength (or multiple thereof) of a sound w-ave travelling longitudinally in the material of the bar at the intended operation frequency. It will be noted that the fluid medium of the system is constantly present in the chamber 61 leading from the fluid passage 51 to the end 80 of bar 60. Cavity 81 is in effect the primary resonator, and bar 69 is the secondary or coupled resonator. It is possible however to so dimension the apparatus that resonance does not occur, as described above, simultaneously in both elements 8.1 and Iat the same frequency. In this latter case only one element resonates. lt is usually preferable to have the double simultaneous resonator combination.

In the opera-tion to be described presently, fluid oscillates as indicated by the d-ouble-headed arrow b in the relatively narrow passage region 68, and this region is `a velocity antinode of a wave pattern set up in the fluid flow passage between the nozzle and the end 80 of bar 60 outside conduit 62. This huid space region and the -acoustic wave pattern set up therein may be analyzed as a quarter-wavelength passage, with a velocity node (pressure antincde) in the chamber S1 adjacent rod 8i?, or may be treated as a Helmholtz resonator as in the case of FlGS. 1 and 2. Thus, the region 63 may be treated as comprising the neck of the resonator wherein oscillating ow takes place, as indicated by the double-headed arrow, while the enlarged space 81 functions las the chamber regio-n thereof. In either case, a resonator is provided.

Operation is as follows: assuming liquid flow inwardly into passage 51 and through nozzle `53:, and assuming that flow is rst via the passage region 68, to one side of conduit 64, at the time of flow inwardly into chamber 8l, fluid flows inwardly into port tube 77, and this flow is transmitted via bores 69 and 72 to enter passa-ge 5l in a lateral direction, so as to impinge on the main fluid stream. Again, as in FIG. 1, the return passage constituted by port tube 77, bore 69 and bore 72 is designed to have an acoustic impedance, for the operating frequency, such as to introduce a predetermined time delay of a duration such that the lateral pressure pulse becomes fully effective at the discharge end -of bore 72 at or near the time of pressure peaking within chamber 81 adjacent rod 80. Accordingly, at such time, the fluid stream issuing from nozzle 53 is deflected so as to enter the open end of conduit 62. Fluid flow then takes place inwardly of port tube 73, and via bores and 73 to create la lateral pressure pulse against the fluid stream in its last described position. Again, fluid port 78 and bores 70 and 73 are designed with an acoustic impedance laffording time delay. When, however, the pressure pulse appears at the exit oriiice of passage 73, the iiuid stream is deflected back to its initial di-rection, so as to flow again into passage 68. The time delay introduced by the last mentioned return passage is such that the last mentioned switchover of the fluid stream occurs in step with fluid flow in the forward direction in the region 68, in accordance with the oscillating ow condition set up in said region by reason of the resonator action of passage 68 and chamber 81. The operation in this respect is entirely analogous to that described in connection with FIG. 1.

It is important to recognize that we are dealing with the elastic acoustic properties of the fluid. The pulses in 65 and 68, as well as 69 and 7%, are substantially sinusoidal.

Pressure pulsations are thus set up adjacent and against the end Si of bar 61 at the resonant frequency of the resonator 68, 8l. These pressure pulses applied against the end of rod Si set up `alternating waves of compression and tension travelling the length of rod 80 with the speed of sound, These waves 'are reliected from the opposite end of rod 8i), and by interference with the forwardly travelling waves, a longitudinal resonant standing wave is set up in the rod, each halfportion thereof alternately elastically elongating yand contracting in step with pressure oscillations occurring in chamber 81 at the resonating frequency of the resonator 68, 81. It has been mentioned heretofore that the resonating frequency of bar 80 for half-wave standing wave vibration is matched to the resonating frequency of resonator 68, 81. Under such conditions, the bar Sil can be set into standing wave vibration at substantial amplitude, and its forward extremity 82 becomes a powerful source of sound wave radiation into an elastic medium in Contact therewith or coupled thereto. Furthermore, end 82 has many other uses as a source of powerful vibrations, such as in drilling, or in various mechanical applications employing vibratory energy.

It Will be understood that the drawings and descriptions are merely illustrative of the invention, and that various changes in design, structure and arrangement may '2" be made without departing from the spirit and scope of the invention and `of the broader of the appended claims.

What is claimed is:

1. In a sonic generator, the combination of: a uid conduit having divergent branches between which fluid flowing through said conduit may be switched, a resonant fluid chamber containing an elastic fluid body connected to `at least one of said branches, and means comprising fluid pressure pulse means operable at the resonant fre quency of said chamber connected into said uid conduit in the region of said branches in lateral pressure transmitting relation to said fluid stream for switching fluid fiow at said resonant frequency ybetween said branches, so that said fluid body undergoes elastic vibration at the resonant frequency of said chamber in respouse to periodic fiuid flow delivered into said chamber.

2. In a sonic generator, the combination of: a fluid conduit having divergent branches between which fluid flowing through said conduit may be switched, an elastic resonator coupled to at least `one of said branches and responsive to periodic fluid flow therein and means cornprising fluid pressure pulse means operable at the resonant frequency of said resonator connected into said fluid conduit in the region of said branches in lateral pressure transmitting relation to said fluid stream for switching fluid flow at said resonant frequency between said branches so as to cause elastic vibration of said resonator in response to periodic fluid flow in said one branch.

3. The subject matter of claim 1, wherein said resonant fluid chamber comprises walls defining a Helmholtz resonator.

4. The subject matter of claim 1, wherein said resonant fluid chamber includes a wall dening a pressure antinode region, and an elastic sound wave radiator within said wall having an interior surface inside said chamber exposed to said pressure antinode region and an opposed sound radiator surface exterior of said chamber.

5. The subject matter of claim 4, wherein said radiator comprises an elastic diaphragm.

6. The subject matter of claim 4, wherein said radiator comprises an elastic rod of substantially half wave length for the resonant frequency of said resonant chamber, a quarter wavelength portion of said rod being enclosed within said chamber, with the extremity thereof in said pressure antinode region of said chamber.

7. The subject matter of claim 1, wherein said resonant fluid chamber comprises a tapered chamber substantially in the form of an exponential horn, and an elastic diaphragm closing the large end of said horn.

8. In a sonic generator, the combination of: a fiuid conduit having two divergent branches between which fluid flowing through said conduit may he switched, an elastioally resonant uid chamber connected to at least one of said branches, said resonant 'fluid chamber having a velocity antinode region, and means for switching uid flow between said branches comprising a feed back con duit coupled at one end to the velocity antinode region of said chamber and directed at the other end laterally into said first mentioned conduit at a first point upstream of said branches 4and on the -side of said conduit corresponding to the branch to which said resonant chamber is connected for feeding time-delayed pressure pulses from said velocity antinode region of said chamber to said first point in said first mentioned conduit, and a feed back conduit coupled at one end to the other of said conduits and directed at the other end laterally into said conduit at a second point upstream of said :branches and on the side of said conduit corresponding to said other branch for feeding time-delayed pressure pulses from within the `other `of said branches to said second point in said first mentioned conduit, said time delayed pulses being adjusted to the resonant frequency of said chamber.

9. The subject matter of claim 1, wherein said branches are vtwo in number, and a resonant chamber is connected to and forms va part of each of said branches.

10. The subject matter of claim 2, wherein said elastic resonator comprises an elastic resonant rod adapted to `have a longitudinal resonant standing wave set up therein, with a velocity antinode at each of its ends and arranged with one of its ends fluid coupled to said branch.

1l. The subject matter of claim l, wherein said divergent branches have Walls defining flow directing surfaces over which said fluid flows in conforming hydrodynamic flow paths generally parallel to or along said surfaces in the manner of flow Yalong a hydrofoil.

References Cited in the le of this patent UNITED STATES PATENTS 1,303,939 Moellmer May 20, 1919 2,138,051 Williams Nov. 29, 1938 2,532,229 Horsley Nov. 28, 1950 2,559,864 Firth July 10, 1951 2,859,726 Bouyoucos Nov. 1l, 1958 

1. IN A SONIC GENERATOR, THE COMBINATION OF: A FLUID CONDUIT HAVING DIVERGENT BRANCHES BETWEEN WHICH FLUID FLOWING THROUGH SAID CONDUIT MAY BE SWITCHED, A RESONANT FLUID CHAMBER CONTAINING AN ELASTIC FLUID BODY CONNECTED TO AT LEAST ONE OF SAID BRANCHES, AND MEANS COMPRISING FLUID PRESSURE PULSE MEANS OPERABLE AT THE RESONANT FREQUENCY OF SAID CHAMBER CONNECTED INTO SAID FLUID CONDUIT IN THE REGION OF SAID BRANCHES IN LATERAL PRESSURE TRANSMITTING RELATION TO SAID FLUID STREAM FOR SWITCHING FLUID FLOW AT SAID RESONANT FREQUENCY BETWEEN SAID BRANCHES, SO THAT SAID FLUID BODY UNDERGOES ELASTIC VIBRATION AT THE RESONANT FREQUENCY OF SAID CHAMBER IN RESPONSE TO PERIODIC FLUID FLOW DELIVERED INTO SAID CHAMBER. 